Decontaminating metal surfaces

Abstract

This invention relates to an electrolyte and an electrolytic method for removing radioactive contaminants from the surface of a metallic substrate.

We claim: 
     
       1. A process for decontaminating an object having a surface contaminated with a radioactive substance comprising: contacting said object with a basic aqueous solution containing nitrate, fluoride, borate, and oxalate anions; thereafter electrolytically removing a surface layer of said object; and subsequently separating resulting precipitate from said solution. 
     
     
       2. The process of claim 1 further comprising reusing said solution after said separating said precipitate. 
     
     
       3. The process of claim 1 wherein the basic aqueous solution comprises from 50 to 500 g/1 NaNO 3 , from 0.1 to 2.5 g/1 NaF, from 1 to 20 g/1 Na 2  B 4  0 7  ·1OH 2  O, and from 0.1 to 4 g/1 Na 2  C 2  O 4  ; said solution having a pH from 7 to 11. 
     
     
       4. The process of claim 2 wherein the basic aqueous solution comprises about 200 g/1 NaNO 3  about 2 g/1 NaF, about 20 g/1 Na 2  B 4  O 7  ·1OH 2 , and about 2 g/1 Na 2  C 2  O 4  ; said solution having a pH about 9. 
     
     
       5. The process of claim 1 wherein said electrolysis is conducted with a potential of from 4 to 24 volts, a current density of from 1 to 8 amps/in 2 , and at a temperature of from 25° to 90° C. 
     
     
       6. The process of claim 1 wherein the object is of an alloy including at least one of the metals iron, chromium, nickel, aluminum, copper, or lead and the radioactive substance is an actinide. 
     
     
       7. The process of claim 1 wherein the metal object is stainless steel and the radioactive substances is plutonium or americium. 
     
     
       8. A basic aqueous solution for electrochemical machining comprising from 50 to 500 g/1 NaNO 3 , from 0.1 to 2.5 g/1 NaF, from 1 to 20 g/l Na 2  B 4  O 7  ·1OH 2  O, and from 0.1 to 4 g/1 Na 2  C 2  O 4 .